Technical Field
The present disclosure relates to light-emitting diode (LED) lamps that work with conventional fluorescent lamp fixtures originally configured to electrically connect to ballasts.
Description of the Related Art
Solid-state lighting from semiconductor light-emitting diodes (LEDs) has received much attention in general lighting applications today. Because of its potential for more energy savings, better environmental protection (with no hazardous materials used), higher efficiency, smaller size, and longer lifetime than conventional incandescent bulbs and fluorescent tubes, the LED-based solid-state lighting will be a mainstream for general lighting in the near future. Meanwhile, as LED technologies develop with the drive for energy efficiency and clean technologies worldwide, more families and organizations will adopt LED lighting for their illumination applications. In this trend, the potential safety concerns such as risk of fire become especially important and need to be well addressed.
In today's retrofit application of an LED lamp to replace an existing fluorescent lamp, consumers may choose either to adopt a ballast-compatible LED lamp with an existing ballast used to operate the fluorescent lamp or to employ an AC mains-operable LED lamp by removing/bypassing the ballast. Either application has its advantages and disadvantages. In the former case, although the ballast consumes extra power, it is straightforward to replace the fluorescent lamp without rewiring, which consumers have a first impression that it is the best alternative. But the fact is that total cost of ownership for this approach is high regardless of very low initial cost. For example, the ballast-compatible LED lamps work only with particular types of ballasts. If the existing ballast is not compatible with the ballast-compatible LED lamp, the consumer will have to replace the ballast. Some facilities built long time ago incorporate different types of fixtures, which requires extensive labor for both identifying ballasts and replacing incompatible ones. Moreover, a ballast-compatible LED lamp can operate longer than the ballast. When an old ballast fails, a new ballast will be needed to replace in order to keep the ballast-compatible LED lamps working. Maintenance will be complicated, sometimes for the lamps and sometimes for the ballasts. The incurred cost will preponderate over the initial cost savings by changeover to the ballast-compatible LED lamps for hundreds of fixtures throughout a facility. In addition, replacing a failed ballast requires a certified electrician. The labor costs and long-term maintenance costs will be unacceptable to end users. From energy saving point of view, a ballast constantly draws power, even when the ballast-compatible LED lamps are dead or not installed. In this sense, any energy saved while using the ballast-compatible LED lamps becomes meaningless with the constant energy use by the ballast. In the long run, the ballast-compatible LED lamps are more expensive and less efficient than self-sustaining AC mains-operable LED lamps.
On the contrary, an AC mains-operable LED lamp does not require a ballast to operate. Before use of the AC mains-operable LED lamp, the ballast in a fixture must be removed or bypassed. Removing or bypassing the ballast does not require an electrician and can be replaced by end users. Each AC mains-operable LED lamp is self-sustaining. Once installed, the AC mains-operable LED lamps will only need to be replaced after 50,000 hours. In view of above advantages and disadvantages of both the ballast-compatible LED lamps and the AC mains-operable LED lamps, it seems that market needs a most cost-effectively solution by using a universal LED lamp that can be used with the AC mains and is compatible with a ballast so that LED lamp users can save an initial cost by changeover to such a universal LED lamp followed by retrofitting the lamp fixture to be used with the AC mains when the ballast dies.
However, most of the LED lamp users will choose to use ballasts as their first choice without caring about the operation of the AC mains because of a budget issue. In some applications, recessed can lights and sconces use an old type of compact fluorescent lamp (CFL), also known as PL lamp, which is frequently confused with a new generation of CFL lamps. Lighting manufacturers want to sell them because once an end user buys a fixture associated with a specific type of PL lamp, she or he will be locked into buying such a type of lamps forever.
The new generation CFL lamps, having a spiral looking, use a common Edison (or medium) base that can screw into any common light socket to operate, thus widely being accepted to replace outdated incandescent bulbs to save energy, run cooler, and last longer. With a ballast built in, this new type CFL lamp features no-lead glass and will work in any position, base up, down, or horizontal. In some applications, these new CFLs will be modified to use a newer GU-24 base designed to prevent the end users from changing back to incandescent bulbs to meet government policy requirements. Nevertheless, millions of old style CFL lamps do not have a built-in ballast but a remote one located separate from the lamps. It has a base with pins protruding from the bottom, to plug in to the corresponding socket to work. In many of such an application, the ballast would usually be located somewhere inside the fixture. But in a recessed can light, the ballast will be on the top or side of the fixture, located in the ceiling between the rafters. It is not accessible from below, where one would normally be replacing a lamp. The average maintenance person is not supposed to go into the ceiling to walk the rafters and find a particular fixture in a particular room. In most cases, insulation will be covering the fixture in the attic, making it difficult to locate and remove an old ballast. This is why the LED lamp users will choose to use ballasts as their first choice.
The PL lamps have so many models with bases having different configurations, rated power, and numbers of pins. They are not interchangeable. For example, two-pin lamps cannot replace four-pin ones due to different startup processes/configurations to operate the lamps. A lamp with a larger rated power cannot replace one with smaller rated power, or a ballast fire may occur. Essentially, they all rely on external ballast that is installed in the fixture. Besides, it is difficult to obtain replacement bulbs because there are too many models for a store to stock all. Fortunately in the US, most of ballasts in lamp fixtures are types of electronic ballasts because they are more efficient than other types of ballasts. In electronic ballast category, there are only two types: rapid-start and instant-start. As a replacement lamp, a ballast-compatible LED lamp must be compatible with existing ballasts which are either rapid-start electronic ballasts with four outputs or instant-start with two outputs.
As mentioned above, a cost-effective solution may be to use a ballast as part of an LED driver to operate an LED lamp. For an LED lamp operating solely with a ballast, the power and current control is basically via an impedance or output voltage control. In the former case, when input frequency changes, the impedance changes, altering an AC current to flow into a driving circuit to operate the LED lamp. A ballast is, in practice, supposed to operate two or more lamps, and its output frequency of the ballast decreases as a load increases, meaning that the total power consumption does not linearly increase as the number of lamps used increases. In the worst case, an LED lamp that is designed for a group of two or three lamps in a fixture powered by a ballast may be burned out due to over-rated current flowing into LED arrays in the lamp if only one of such a lamp is installed in the fixture. For the latter case, the output voltage control approach may work with an electronic ballast. In general, conventional LED drivers sometimes fail to work with a ballast and to properly operate an LED lamp at a regulated power, resulting in unstable lighting output.
In this disclosure, the LED lamps operating with an AC power source are proposed, which are allowed to plug directly into a ballast or an AC mains driven fixtures, avoiding extra expense and disruption associated with replacing or modifying an existing light fixture to capture the benefits of LED lighting.